1. Field of the Invention
The present invention relates to a pressure regulator for use with a fuel cell for controlling the amount of an oxidizing agent discharged from a cathode of a fuel cell stack thereby to regulate the flow rate or pressure of the oxidizing agent that is supplied to the cathode.
2. Description of the Related Art
A solid polymer membrane fuel cell has a stack of cells each comprising an anode and a cathode, and a solid polymer electrolyte membrane interposed between the anode and the cathode. Hydrogen is supplied as a fuel to the anode of each cell and air is supplied as an oxidizing agent to the cathode of each cell. Hydrogen ions that are generated at the anode by a catalytic reaction move through the solid polymer electrolyte membrane to the cathode. Electric power is generated in the fuel cell by the electrochemical reaction.
A fuel cell system which includes such a stack has an air compressor for supplying air to the cathodes and a pressure control valve for supplying hydrogen to the anodes under a pressure depending on the pressure of air which is given as a signal pressure. The pressure of the reactant gas supplied to the anodes with respect to the pressure of the reactant gas supplied to the cathodes is adjusted to a predetermined pressure for thereby achieving a predetermined power generation efficiency, and the flow rate of the reactant gas supplied to the fuel cell stack is controlled to obtain a desired fuel cell output.
In such solid polymer membrane fuel cell devices, the flow rate or pressure at which the air is supplied is regulated in order to adjust the pressure applied to the solid polymer electrolyte membrane and the differential pressure between the anode and the cathode. Specifically, a discharge line for discharging an unreacted oxidizing agent gas and H2O generated by electric power generation from the cathode has a pressure regulating valve for regulating the pressure in the cathode (see Japanese laid-open patent publication No. 2001-176526 and Japanese laid-open patent publication No. 2002-313382).
The pressure regulating valve generally comprises a butterfly valve. When a control motor for opening and closing the valve body of the pressure regulating valve is not energized, the valve body is urged by a spring to move in a direction to be closed. When the control motor is energized, it turns in a direction to open the valve body against the resiliency of the spring. Therefore, the pressure regulating valve is a normally closed valve.
If the fuel cell system is mounted on an automobile or the like, for example, then the pressure regulating valve is used in an open state while the automobile is stably running. With the pressure regulating valve being a normally closed valve, therefore, the control motor needs to be energized at all times in order to open the valve while the automobile is running.